linux-kernel - Re: Page Faults slower in 2.6.25-rc9 than 2.6.23

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Message-ID: <661de9470804290752w1dc0cfb3k72e81d828a45765e@mail.gmail.com>
Date:	Tue, 29 Apr 2008 20:22:58 +0530
From:	"Balbir Singh" <balbir@...ux.vnet.ibm.com>
To:	"Hugh Dickins" <hugh@...itas.com>
Cc:	"Ross Biro" <rossb@...gle.com>, linux-mm@...ck.org,
	lkml <linux-kernel@...r.kernel.org>,
	"Kamalesh Babulal" <kamalesh@...ux.vnet.ibm.com>
Subject: Re: Page Faults slower in 2.6.25-rc9 than 2.6.23

On Tue, Apr 29, 2008 at 7:27 PM, Hugh Dickins <hugh@...itas.com> wrote:
> On Tue, 29 Apr 2008, Ross Biro wrote:
>  > I don't know if this has been noticed before.  I was benchmarking my
>  > page table relocation code and I noticed that on 2.6.25-rc9 page
>  > faults take 10% more time than on 2.6.22.  This is using lmbench
>  > running on an intel x86_64 system.  The good news is that the page
>  > table relocation code now only adds a 1.6% slow down to page faults.
>
>  Do you have CONFIG_CGROUP_MEM_RES_CTLR=y in 2.6.25?
>  That added about 20% to my lmbench "Page Fault" tests (with
>  adverse effect on several others e.g. the fork, exec, sh group).
>

Hmm.. strange.. I don't remember the overhead being so bad (I'll
relook at my old numbers). I'll try and git-bisect this one


>  Try the same kernel with boot option "cgroup_disable=memory",
>  that should recoup most (but not quite all) of the slowdown;
>  or rebuild with n to CGROUP_MEM_RES_CTLR.
>
>  But your "Mmap Latency" went up 425% ??
>

That's really way of the mark

>  Hugh
>

Balbir
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